The present invention relates to a recording and reproducing apparatus and a magneto-optical recording medium for use therewith in which the magneto-optical recording medium includes a substrate layer, a reflective film layer, a magneto-optic recording film layer and a transparent protective layer. The present recording and reproducing apparatus may include a magnetic coil arranged on a surface which faces the magneto-optic recording film and an optical system arranged such that its optical axis traverses the center of the magnetic coil. Such magnetic coil and optical system may be arranged on the transparent protective layer side of the magneto-optical recording medium when the recording medium is being used with the recording and/or reproducing apparatus. As a result, the present recording and/or reproducing apparatus enables acceptable recording and reproducing signals to be provided.
A magneto-optic disc may include a transparent substrate having a thickness between 0.6 to 1.2 mm. Such magneto-optic disc may further include a transparent dielectric film which may be formed from silicon nitride, aluminum nitride, silicon oxide and/or ZnS by a so-called sputtering or a vacuum depositing operation on a surface of the transparent substrate;
photomagnetic recording films including amorphous rare earth metal magnetic films such as TbFeCo, GdFeCo, DyFeCo or TbFeCoCr, or perpendicular recording films such as PtCo which may be recorded or formed by a sputtering or vacuum depositing operations; an Al-based metal reflective film mainly composed of Al, AlTi or AlCr which may be formed by a sputtering or vacuum depositing operation; and a transparent protective layer of a UV-curable resin which may be formed by a so-called spin coating operation.
To record information on the above-mentioned photomagnetic recording medium, light is radiated from an optical system through the transparent substrate having a thickness between 0.6 to 1.2 mm to the recording medium so as to produce a phase change thereof. At the same time, a magnetic field is applied by a magnetic head from the opposite side of the transparent substrate. Such magnetic field may be modulated with the information by use of a magnetic field modulation device. As a result, the information may be recorded on the recording medium. To reproduce the information from the photomagnetic recording medium, light is also radiated by the optical system through the transparent substrate. In this situation, the optical system is arranged on the transparent substrate side of the disk.
Recording density may be improved by reducing the optical spot diameter. Such reduction may be achieved by increasing the value of the numerical aperture (NA) of the optical system such as to a value greater than 0.8.
However, if the numerical aperture NA of the optical system is increased as described above, the thickness of the transparent substrate (through which the irradiated light beam passes) may need to be reduced. More specifically, if the numerical aperture NA is increased, then the allowance of the angle by which the disc surface is deviated from the perpendicular with respect to an optical axis of the optical system (tilt angle) is reduced under the effect of double refraction or aberration due to the thickness of the transparent substrate. Accordingly, to reduce the effect of the tilt angle, the thickness of the transparent substrate should be decreased.
However, if the thickness of the transparent substrate is reduced as described above, and if the magnetic field is applied by the magnetic head from the transparent protective layer side, sufficient magnetic field strength may not be achieved because of the increased distance to the photomagnetic or magneto-optic recording film.
In an attempt to overcome the above mentioned problem, a recording and reproducing apparatus may be utilized wherein the magnetic head is provided between the transparent substrate and the optical system, thereby decreasing the distance between the magnetic head and the photomagnetic or magneto-optic recording film. However, even with such apparatus, if the transparent substrate has a thickness of 100 .mu.m and the separation gap between a surface of a magnetic coil of the magnetic head which faces the transparent substrate and the surface of the transparent substrate or the surface of the magneto-optic disc is set to 100 .mu.m, it may not be possible to provide a magnetic field having sufficient strength (for example, approximately 1500 Oe) for recording and reproducing signals. Further, to increase the strength of the generated magnetic field by use of this recording/reproducing apparatus, it may be necessary to increase the power supplied thereto in order to increase the strength of the generated magnetic field. As a result, the power consumption by the recording and reproducing apparatus may be increased which may cause circuitry to be damaged due to excessive heating and the associated mechanical or electrical overloads.